Compilers: Principles and Practice by Pearson

Code Optimization 321

The value of i * 5 can be saved in a temporary t, whose value is incremented by 5 for each iteration

of the loop, as

i = 1;

t = 5;

while(i < 100){

// some code

a = t;

// some code

i++; t += 5;

}

This replaces a multiplication by an addition.

10.3.2 Constant Folding

In this method, the compiler itself does as much of the computation as possible. If any expression

or a part thereof contains only numeric constants, then the compiler can easily calculate the value

at compile-time and generate the code only for the resultant value. Even the Parser, before the

semantic phase, can do this computation. For example, an expression ...